Catalytic conversion systems employing fluidized solids



Patented Sept. I4, 1948 CATALYTIC CONVERSION SYSTEMS EMPLOYING FLUIDIZED SOLIDS Harry K. Wheeler, Jr., and Robert J. Hengstebeck, Chicago. Ill., assignors to Standard Oil diana Company, Chicago, 111., a corporationiot In- Application March 29, 1945, Serial No. 585,490

4 Claims. (Cl. 196-52) This invention relates to catalytic conversion systems employing fluidized solids and it pertains more particularly to improved methods and means for recovering catalyst solids from gasiform streams. In adivisional application Serial No. 2,434 filed by Harry K. Wheeler, Jr., on January 15. 1948, the claimed invention relates to the comb nation of solids removal of utilization of potential energy of one of said streams.

Our invention is applicable to any catalytic conversion system wherein solid catalyst material .pense and with maximum conservation of valuable charging stock and product components.

In catalytic cracking systems employing fluidized solids as catalyst materials it has been the practice to recover solids from the eiliuent product stream in a scrubbing zone which forms the lower part of an initial fractiozating zone, a portion of the solids-containing bottoms from the scrubbing zone being recycled through a cooler to the upper part of the scrubbing zone above the hot be recovered from regeneration gases by countercurrent scrubbing with at least a portion of the feed stock (U. S. Patents 2,273,0'75-6). In such a process however a certain amount of the valuable feed stock is lost by vaporization and there is a tendency toward oxidation of valuable charge components by residual oxygen in the regeneration gas. An object of our invention isto provide an improved method and means for recovering solids from regeneration gases and for avoiding the necessity of any contacting of hot regeneration gases with incoming charging stock. A

product inlet; An object of our invention is to avoid the recycle oi' solids-containing liquids and to employ a substantially solids-free oil as a cooling and scrubbing agent in the scrubbing zone or zones.

That portion of the solids-containing liquid which has been withdrawn from the base of the scrubbing zone has heretofore been returned with charging stock to the catalytic cracking conversion zone. It was found however that the return of this material leads to the deposition of unduly large amounts of coke on the catalyst in the conversion zone and that the best practice is to settle these solids from the withdrawn solidscontaining liquid andto avoid the return of the bulk of the liquid to the conversion zone. An object of our invention is to improve the process of returning spent catalyst by providing improved methods and means for washing and displacing coke-forming oil from the settled catalyst particles and returning said particles in heavy virgin oil suspension with no substantial amounts of heavy cracked materials.

It has been found that catalyst particles may further object is to accomplish the removal 01' solids from regeneration gases with minimum capital investment and minimum operating costs.

Our invention will be described as applied to the catalytic cracking 01' gas oils or reduced crudes to produce motor fuel but it should be understood that the invention is also applicable to other hydrocarbon conversion processes such as retreating, reforming, hydroforming. aromatization, hydrogenation, dehydrogenation, desuliurization, etc. and in fact to fluidized solids conversion processes generally.-

Our invention contemplates the addition to present fluid-type catalytic cracking systems of one ormore settlers, a regeneration gas scrubber, and pumps, lines and heat exchangers arranged and operated to provide a markedly improvedcatalyst recovery system. Instead o! scrubbing regeneration gas with incoming charge or a portion thereof we employ as a scrubbing medium the low grade residual product fraction preferably ai'ter a substantial amount of its heat has been utilized for generating steam or preheating incoming charging stock. The scrubbing oil for both the product streams and the regeneration gas streams may be substantially free from solids thus improving the solids separation step as well as minimizing erosion on transfer lines, pipes,

heat exchangers, etc. The residual product oil which serves as a scrubbing oil for catalyst removal is not only effectively kept outoi' the charge stream but it is utilized for recovering catalyst from regeneration gases.

The invention will be more clearly understood from the following detailed description of a specific example and from the accompanying drawings which form a part of this specification and in which:

Figure 1 is a schematic flow diagram of our improved catalyst and power recovery system and,

Figure 2 is a. vertical section through our combined settler-steam generator.

Referring to Figure 1, a charging stock such,

to the base of reactor l2. Hot regenerated cat- I alyst from regenerator I3 is introduced by standpipe l4 into transfer line H in amounts sufficient to effect the desired conversion and to supply at' least a considerable portion of the heat required therefor. The catalyst may be of the natural or synthetic silica-alumina type or of any other known type and should preferably have a particle size chiefly within the range of 10 to 100 microns. Spherical catalyst particles are particularly advantageous.

The regenerator in this case may operate at a temperature in the approximate range of 950 to 1100' F., e. g.. about 1000-1050 F., so that if sufficiently large catalyst-to-oil ratios are employed, the contained heat of the catalyst may supply not only the heat of conversion but all or a substantial part of the heat of vaporization of the charging stock. The charging stock may however be suitably preheated and if desired it may be vaporized and preheated to substantially conversion temperature before it picks up the catalyst from the base of standpipe Hi. The flow of catalyst through standpi e l4 may be. regulated by valve i5 and the catalyst, in the standpipe may be maintained in aerated liquid-like condi- 4 light dispersed phase. A portion of the dense phase catalyst may be recycled through standpipe 30 and cooler 8! to maintain regeneration temperature within desired limits. Cyclone seption by the introduction of aeration gas through line it.

The suspension of regenerated catalyst in incoming charging stock is distributed in reactor 12 by means of grid I1 and a vertical gas or vapor velocity in the reactor is maintained in the approximate range of about 1 to 3 feet per second so that a suspended dense turbulent phase of catalyst is maintained in the reactor, which dense phase is superimposed by a light dispersed phase. Catalyst may be knocked back from the light phase to the dense phase by means of cyclone separators i8 or other known means, the gasiform product being withdrawn overhead through line l to the base of scrubber 20 which forms the lower part of fractionating tower 2|. Reactor i2 may be operated under any desired conversion conditions. conversion temperatures usually being within the approximate range of 800 to 1000 F. for example about 925 F. and the pressure bein within the approximate range of about atmospheric to about 10 atmospheres. The weight ratio of catalyst-to-oll in the suspension introduced into the reactor may be within the approximate range of 1:1 to :1; the residence time of the catalyst in the reactor may be within the approximate range of about 2 to 200 minutes and the weight space velocity will be within the approximate range of .2 to 20 pounds of charging stock introduced per hour per pound of catalyst maintained in the reactor.

Catalyst is withdrawn directly from the dense phase in reactor i2 into stripping zone 22 wherein it is stripped with steam or other strippinggas introduced through line 23. The stripped catalyst passes downwardly in standpipe Z L-is maintained in fluent liquid-like form therein by aeration gas introduced through line 25 and is dispersed from the base of the standpipe through valve 26 into conduit 21 wherein the catalyst is suspended in air introduced from line 28 and the suspension is carried to the base of regenerator l3. The suspension is distributed in regenerator I3 arators 32 or other suitable means may be employed to knock back catalyst from the dilute phase to the dense phase. Hot regeneration gases are removed from the regenerator by line 33. The system thus far described is conventional fluid type catalytic cracking. Our inveniton is not limited to this particular system but is applicable to any fluidized solids conversion system that. Dresents the problem of recovery solids and heat or energy from eilluent gaslform streams. More detailed descriptions of such systems and of the catalyst conditions employed therein are set forth in U. 8. Patents 2,337,684 and 2,341,193 and in numerous copending applications.

For recovering solids from a product stream a substantially solids-free non-volatile oil may be cooled in heat exchanger 34 (although such cooling, 1. e. the use of such heat exchanger is not always necessary) and introduced through line 35 at the upper part of scrubber 20 which may be provided with suitable bailles 36. Oil introduced through line 35 effects the condensation of the highest boiling components of the product stream and simultaneously scrubs the solids out of said stream. Components of the gas oil boiling range together with lower boiling'components pass upwardly from the scrubbing section 20 to the rectifylng or fractionatlng portion of tower II from which a heavy gasoil stream may be withdrawn through line 3'! and alight gas oil stream through line 38. Gasoline boiling range components, steam and normally gaseous materials are taken overhead through line 39 for fractionation and recovery in the usual manner.

The hot scrubbing oil, condensate, and suspended solidsare withdrawn'from the base of scrubber 20 through line 40. A heat exchanger for incoming charging stock or waste heat boiler 4| may be employed for cooling the withdrawn liquid to a temperature of the order of 300 to 600 F. although as described in connection. with Figure 2, such cooling may be effected in the settlin zone after solids have been separated from the liquids. With valve 42 open, .valves'43 and 44 closed, the slurry of recovered catalyst solids may be introduced into settling chamber 45. Settled solids may be withdrawn from the inclined bottom of the settling chamber as a thickened slurry I through conduit 46 and returned through line 4'! to charging stock inlet line ID. A portion of the charging stock may be introduced through line 48 for facilitating transfer of the solids. If desired the slurry from line 46 may be introduced by line 49 to a washing zone along with a relatively clean non-coke-forming oil and the catalyst may be settled from such relatively clean oil before recycle in order to eliminate more completely the return of coke-forming oil with recycled catalyst.

Substantially solids-free oil is withdrawn from settler by line 50 and at least a substantial part of this withdrawn oil is introduced by .Dump 5| and line 35 back to the upper part of scrubbing by means of grid 29 and upflowing gas velocities of about 1 to 3 feet per second are employed to maintain the catalyst in the regenerator as a suspended dense turbulent phase superimposed by a zone 20. The remainder of the solids-free all may be withdrawn from the system through line 52 and it is preferably introduced by pump 53 and line 54 to the upper part of scrubber 55 which may be provided with suitable bailies or other means for securing effective gas-liquid contact. Regeneration gas from line 33 is introduced at the base of scrubber 55. When the potential energy in the regeneration gas stream is to be utilized duced at the base 01' scrubber 55 directlyfrom the top 01' the regenerator and without any appreciable cooling. However, we may employ a waste heat boiler and we may by-pass allor a sumcient part of the regeneration gas through said waste heat boiler, materially reduce the temperature of gases entering scrubber 5-5 and generate high pressure steam. The temperature or the gases entering the base of scrubber 55 is preferably within the range of about 600 to 1200 1 and for example may, be about 900 F. to 1000 F. A suflicientamount of oil is introduced through line 54 to scrub out substantially all of the residual solids contained in the regeneration gases.

The scrubbing liquid with accumulated solids is withdrawn through line 51 and heat exchanger or waste heat boiler 58 to settler 59 although here again the waste heat boiler may be built into the settler itself as described in connection with Figure 2. The settled catalyst solids are withdrawn from the settler through conduit 60 and may be returned by lines BI and 41 to line ill or introduced by lines 5| and 62 to settler 45. Alternatively these solids may be washed in a separate washing -zone before recycling, Relatively clean non-coke-forming oil, or a portion of the charging stock, or oil from line 52 may be introduced through line 53 to facilitate the handling and/or washing of the solids.

A portion of the solids-free oil withdrawn from settler 59 through line 84 may be recycled by 'pump 65 and line 54 to scrubber 55, the net pro- I through line 6-8.

v By providing separate settlers 45 and 59 for scrubbers 20 and 55 respectively in the manner hereinabove described the product stream is not contaminated by oils which have been contacted and perhaps partially oxidized with the regeneration gas stream. However, when such oxidation presents no problem we may dispense entirely with settler 45 and pass the solids-containing oil from line 40 through valve 43 into settler 59. In this case a portion of the clear oil from line 64 is returned by pump 61 to line 35 for recycle through cooler 34 to the upper part of scrubber 20. We may pass the solids-containing liquid from line 40 through valve 44 and lines 68 and 54 directly to the upper part of scrubber 55 but such alternative is open to the objection that the oil introduced at the top of scrubber 55 would contain solids. Our preferred method of operation for scrubbing oil is substantially freed from solids and hence'is more efficient for removing solids and less likely to cause erosion, line plugging. etc.

The hot regeneration gases leaving the topof scrubber 55 may be introduced by lines 69. 10. and H directly to turbine 12 for generating electrical energy, driving air compressors or otherwise utilizing potential energy of this gas stream. The removal of solids in scrubber 55 prevents the erosion of turbine blades and parts.

When spherical catalyst particles are employed and such particles are substantially quantitatively removed from regeneration gases by cyclones 32 or other separation means the use 01' scrubber 55 may be unnecessary and the hot regeneration gases may be introduced directly to leaving the crubber through line 69. To utilize or for driving compressors Catalyst solids are removed through conduits 60a the potential energy of this gas stream we may pass it through line I4 through one of the oxidizing chambers 15 and 1511 (into which an air stream can be introduced through line 15 ii additional oxygen is necessary) for effecting'combustion of the hydrocarbon vapors in the gas stream that were picked up in the scrubber and for materially increasing the temperature of the gases introduced through line H to turbine 12, The oil gases from the turbine may be passed through line 11 through exchanger 15 and the incoming air stream from line 19 may be passed through this exchanger in order to preheat the air. introduced through line 15 to the oxidizing chambers. oxidizing chamber 15 may be open vessels of the type commonly known as flue gas generators or they may be packed with any known type of oxidation catalyst material for insuring substantially product recovery system through line with a corresponding increase in the amount of air introduced through line 16.

By operating our entire system at superatmospheric pressure We can greatly increase the amount of power obtainable from the regeneration gases by the turbine and at the same time efiect savings in equipment costs by employing a smaller reactor, regenerator, etc. Our catalyst recovery system is just as eflicient at low pressures as at higher pressures and may be employed very advantageously in systems wherein the top pressure in the reactor is of the order of 5 to 10 pounds per square inch (gauge pressure). Regenerator pressure is closely tied to reactor pres sure because of the fluids flow system between reactor and regenerator. However, by placing the reactor at a considerably higher level than the regenerator, the top pressure in the regenerator may be 2 to 10 pounds or more higher than the top pressure in the reactor and such an arrangement is desirable for maximum utilization of the potential energy content of the regeneration gases.

As hereinabove stated, we may employ a unitary settler-waste heat boiler assembly as illustrated in Figure 2. In such an assembly the settler 59a may be provided with an upper waste heat boiler section 8| comprising a bundle of tubes 82 secured in headers 83 and 83a. Water enters the upper boiler section through conduit 84 and this section may be provided with staggered bafiles 85 between the water inlet and steam outlet 55. The incoming slurry from line 51a passes under the boiler section and is prevented from short circulating the boiler by extensions 81 of the boiler walls which are secured to the end wall of settler 59a. Solids settle out of the slurry in'the lower part of settler 59a where the temperature of the oil is highest and its viscosity is therefore at a minimum. The solids-free oil then passes through tubes 82 of the waste heat boiler for generating steam which may be employed as process steam in the system or for supplying heat or generators.

and the clear cooled oil streams are withdrawn through lines 54a. Instead of generating steam in section 8| I may use it to preheat incoming charging stock or for heating any other fluids.

While we have disclosed a specific system for recovering solids and energy from gasiform solids leaving Sthe fluidized solids treating system it should be understood that our invention is not limited to the specific arrangements or detailed operations hereinabove set forth since various alternative arrangements and operating conditions will be apparent from the above description to those skilled in the art.

We claim:

1. In a hydrocarbon conversion process e!- tected with fluidized catalyst solids of small particle size wherein both an eiiluent product stream and an eilluent regeneration gas stream contain residual solids. the method of operation which comprises introducing the eiiiuent product stream at the base of a first scrubbing zone, scrubbing solids from said stream in said first scrubbing zone with a heavy hydrocarbon oil scrubbing liquid, introducing at least a part of the scrubbing liquid from said first scrubbing zone into a second scrubbing zone, contacting said regeneration gas stream with said liquid in said second scrubbing zone for recovering solids from said regeneration gas stream, separating solids from said last-named scrubbing liquid and returning at least a part of said separated solids to said hydrocarbon conversion process.

2. The method oiclaim 1 which includes the step of separating solids from the scrubbing liquid 8 steps or discharging scrubbing liquid from both the first and second scrubbing zones into a single settling zone, separating solids from the combined liquids in said settling zone and recycling a part of the separated liquid from the settling zone to the first scrubbing zone and another part of the separated liquid to the second scrubbing zone.

4. The method of claim 1 which includes the steps or introducing the scrubbing liquid from the first scrubbing zone into a first settling zone, separating solids from liquid in the first settling zone, returning a part of the liquid from the first settling zone to the first scrubbing zone, introducing another'part of the liquid from the first settling zone to the second scrubbing zone, introducing solids-containing liquid from said second scrubbing zone to a second settling zone and separating solids from liquids in said second settling zone.

HARRY K. WHEELER, JR. ROBERT J. HENGSTEBECK.

REFERENCES CITED The following references are of record in the file of this patent:

, UNITED STATES PATENTS Name Date Thayer Dec. 16, 1941 Weems Feb. 17, 1942 Schonberg Mar. 6, 1945 Jahnig July 16, 1946 Number 

